Lesson objective: Fluently count on by tens and ones to find sums using base ten blocks and hundred charts.

This lesson helps to build procedural skill whole number addition. Base ten blocks and hundreds charts are used here because they support understanding of counting on by tens and ones. This work develops students' understanding that we can add numbers within 100 using our knowledge of place value.

Students engage in Mathematical Practice 7 as they look for and make use of structure, which is central to the work in this task. Students should identify the structure of place value in order to add or subtract within 100 as they use the base ten blocks or a hundreds chart to count on by tens and ones to add.

**Key vocabulary:**

- counting on
- hundreds chart
- open number line

**Special materials needed:**

- printable hundreds chart included